Of same place



(No Model.) Y

-W. W; DEAN.

TELEPHONE SYSTEM. I

Patented Sept. 24, 1895.

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WILLIAM W. DEAN, OF ST.`LOUIS, MISSOURI, ASSIGNOR TO THEBELIJ TELEPHONECOMPANY OF MISSOURI, OF SAME PLACE.

TELEPHONE SYSTEM.

SPECIFICATION forming part of Letters Patent No. 546,731, datedSeptember 24, 1895. Application led May 18, 1895. Serial No. 549,777.(No model.)

To all whom it may concern,.-l

Be it known that I, WILLIAM W. DEAN, a citizen of the United States,residing at St. Louis, in the State of Missouri, have invented a certainnew and useful Improvement in Telephone Systems, (Oase No. 5,) of whichthe following is a full, clear, concise, and exact description,reference being had to the accompanying drawings, forming a part of thisspecification.

My invention relates to a telephone system, and its object is to provideimproved .switching apparatus at the central station and an improvedform of local transmitter-circuit at the sub-stations.

In an application, Serial No. 539,209, filed February 2l, 1895, I havedescribed a telephone system in which a local transmitter-circuit isprovided at each sub-station comprising two parallel branches, in whichare contained the microphone and the primary windings ofinduction-coils, the secondary windings being included in circuit' withthe telephone-line, which extends in a metallic circuit to the centralstation. At the central station switching apparatus is provided, adaptedto connect the line with another line for conversation, the switchingapparatus serving to unite the two limbs of the metallic-circuit at thecentral station and to connect the same to a grounded battery-current,thus traversing the two limbs of the telephone-line in parallel andpassing through the two branches of the local transmitter-circuit toground at the sub- "In accordance with the present invention, I providein the cord-conductors, employed for looping two lines together forconversation, a repeating-coil, thus isolating the two lines andrendering it possible to connect the metallic circuit and grounded lineswithout unbalancing the talking-circuit. .The windings oftherepeating-coil are connected at the middle with the grounded battery,whereby current from the battery mayl traverse the two limbs of thecircuit in parallel, the clearing-out indicators, one foreach of theconnected subscribers, being included between the windings of therepeating-coil and ground, whereby the entire current passing over anyparticular telephoneline traverses the clearing-out annunciator.

In said application I have describeda form of local transmitter-circuitin which the primary winding of an induction-coil is included in each ofthe two parallel branches constituting the circuit, the secondarywindings being included in series in the telephone-line, whereby thecurrents induced in the windings of the two coils are added.

It is the object of the present invention, in this particular, toprovide means whereby a single induction-coil may serve the purpose ofthe two coils illustrated in said application, the primary winding ofthe induction-coil being connected with the line at an intermediatepoint, wherebya portion of the winding is included in each of theparallel branches, as will be more particularly described hereinafter.

Referring to the accompanying drawings, Figure lis a diagramillustrating two telephone-lines connected together after the manner ofmy invention. Fig. 2-is a similar view illustrating modifications of thelocal transmitter-circuit at the sub-stations.

Like letters refer to like parts in both figures.

The telephone-line extends in two limbs d a from the substation A to thecentral sta-v tion, the limb ct terminating in a line-spring a2 at thecentral station, while the limb a terminates in a line-spring a3,normally resting upon a contact a4, connected through an individualindicator b and the battery c to ground. The limb d is connected at thesubstation with a telephone-hook d, normally resting upon a contact d',connected through a bell d2 to ground. The limb a terminates in acontact-piece d3, carried upon but insulated from the hook d. When thetelephone is removed from the hook, thehook d closes against contact d4and the contactplate d3 closes against the contact d5. Between thecontacts dtand d5 'are included the secondary e of an induction-coil eand the telephonereceiver f. In-a bridge-wire g is included aretardation-coil g', from the center of which extends a conductor g2 tothe middle point e2 of the primary winding e3 of the inductioncoil e,the said primary winding being; in

eluded in a local transmittervcircuit, in dicated by heavy lines, thelocal ytransmitter` circuit being' connected with ground at the point7L. In one branch of the local transmitter-circuit is included themicrophone k. A portion of the primary winding of the induction coil isthus included in each ot' the branches 7L of the localtransmitter-circuit. The sub-station B is similarly connected with thecentral station by the limbs a a', terminating in line-springs as a?,respectively, the line-spring as normally resting against contact a4,connected through indicator b and battery c to ground. Limbs a a areconnected, respectively, with hook d and contactplate d3 at thesub-station, the hook d being adapted to normally rest upon contact d',connected to ground through the bell cl2. When the telephone is removedfrom its hook, the hook d closes against contact d" and the plate d3against contact d5, between which contacts the primary winding e of theinduction-coil e is included in circuit. Thetelephone-receiverfisincluded in the bridge-wire g. The middle point e2of the primary winding c3 of the induction-coil is connected with themiddle point e4 of the secondary of the inductioncoil by a conductor e5,the point 71 of the local transmittercircuit being connected to ground,whereby a portion of the primary of the induction--coil is included ineach of the Y branches 7L h2 of the local transmitter-circuit.

The microphone k is included in one of the branches of the localtransmitter-circuit. At the central station anumberof pairs of plugs Z mare provided, a repeating-coil o being included in the cord-circuit, onewinding o being connected between the terminals of the plug Z, while theother winding o2 is connected between the terminals of the plug m. Fromthe middle point o3 of the winding o extends a conductor a" to groundthrough the battery c, a clearing-out indicator o being included in theconductor o". Likewise a conductor r2 extends from the middle point 04of winding o2, in which conductor is included the elearing-out indicatorr3. The clearing-out indicators r and r3 are constructed to havesufficient retardation eifect to prevent the leakage of thevoice-currents.

By the arrangement as above described the telephone-lines are completelybalanced, and the interposition of the repeating-coil 0 isolates the twoconnected lines, so that if one of the lines should be from any causeunbalanced it will not altect the balance of the otherline. Furthermore,the provision of the repeating-coil renders it possible to unite ametallic circuit-line with a grounded line without disturbing thebalance of the line. lVhen two lines are connected for conversation, theplugs Zand m are inserted in the spring-jacks of the respective lines,as illustrated, and current iiows from the battery c over the twotelephone-lines in multiple to ground at the sub-stations and back tothe battery through the ground return. Tracing the circuit over the lineat sub-station A, current from battery c passes through the clearingoutindicator o by conductor r to the middle point o3 of the winding o ofthe repeatingcoil, thence by two paths over the limbs a a of thetelephone-line in parallel to the contact-points d d5, thence throughthe bridgeconductor g to the repeating-coil, by conductor g2 to themiddle point c2 of the primary winding e3 of the induction-coil, thenceover the two halves of the induction coil and the two branches 7L h2 ofthe local transmitter-circuit in parallel to the point 7L, and thence toground. The entire current of the battery c, passing over any particularline, thus traverses the clearing-out indicator, and a more effectiveoperation of the indicator may be obtained than when the indicator issituated in one of the strands of the cord-conductors, as indicated bydotted lines. Furthermore, the location of the clearing-out indicatorsin the ground branches o" r2 permits the use of the clearing-outindicators as retardation-coils to prevent the leakage of thevoice-currents.

When, as indicated at sub-station l5, the middle of the primary windingof the induction-coil is connected with the middle of the secondarywinding, the telephone receiver f is preferably included in a bridge, inorder that the line may be balanced. At sub-station C, Fig. 2, I haveillustrated the receiver f as included in series with the secondarywinding of the induction-coil; but in this instance the primary windingis not connected with the middle of the secondary winding, but isconnected at a point such that the rcsistance of the portion of thesecondary winding upon one side ot` the connection is substantiallyequal to the resistance of the portion of the winding upon the otherside, plus the resistance of the telephone receiver, a balance of theline being thus secured.

At sub-station D, Fig. 2, I have illustrated the primary winding of theinduction-coil connected with the end of the secondary winding, theresistance of the secondary Winding being in this instance equal to theresistance of the telephone receiver, wherebya balance of the line iseffected. In this instance the conductor e5, joining the primary andsecondary windings, is not connected with the middle portion of theprimary winding, but is connected to one side of the middle, theresistance of the microphone, plus the resistance of the portion of theprimary winding in that branch, being adj usted to equal the resistanceof the portion of the primary winding in the other branch of the localtransmitter-circuit.

At sub-stations A, B, and C, I have illustrated a resistance p, in thebranch h2 of the local transmitter-circuit, adjusted to equal theresistance of the microphone 7c, whereby the line may be completelybalanced.

Having described n iy invention, what I claim as new, and desire tosecure by Letters Patent, is-` IOO IIO

1. The combination with a telephone line extending in two limbs to thecentral station, said limbs being united at the sub station, of aconnection to ground or a common return from said united limbs at thesub-station, a local transmitter circuit included in said connection andcomprising parallel paths in which are included the microphone and theprimary inductive Winding, switching apparatus at the central stationcomprising a repeating coil, through one winding of which the limbs ofthe telephone line are adapted tobe united a connection to ground fromthe united limbs of said telephone line, a battery and a clearing outindicator included in said connection to ground or common return andmeans for preventing the leakage of voice currents through said groundconnection; substantially as described.

2. The combination with a telephone line extending in two limbs to thecentral station, said limbs being united at the sub-station, of aconnection to ground or common return from said united limbs at thesub-station, a local transmitter circuit included in said connection andcomprising parallel paths in which are included the microphone and theprimary inductive winding, switching apparatus at the central stationcomprising a repeating coil, through one winding of which the limbs ofthe telephone line are adapted to be united, a connection to ground oracommon return from the middle of said winding, a battery and a clearingout indicator included in said ground connection, said indicatorpossessing retardation eiect to prevent the leakage of Voice currents;substantially as described.

3. The Vcombination with a local transmitter circuit, comprising twoparallel branches, of an induction coil, the secondary winding thereofbeing included in the telephone circuit, a portion of the primarywinding thereof being included in each of the two branches of the localtransmitter circuit, a microphone included in said local transmittercircuit and a battery adapted to direct current over the branches ofsaid local transmitter circuit in parallel; substantially as described.

4. The combination with a telephone line, of an induction coil, thesecondary winding thereof being included in circuit with the telephoneline, a local transmitter circuit containing the microphone, the primarywinding of said induction coil being included in said local transmittercircuit, said secondary winding being connected with an intermediatepoint of said primary winding,'and a battery adapted to direct currentover the telephone line and from the point of connection with theprimary winding over the two portions of the primary winding through thetransmitter circuit in parallel; substantially as described.

In witness whereof I have hereunto subscrihedmy name this 13th day ofMay, A. D. 1895.

WM. W. DEAN.

Wi tn esses PATK BYRNE, WM. E. HARKNEss.

